EP0845571A1

EP0845571A1 - Door leaf and door assembly

Info

Publication number: EP0845571A1
Application number: EP97309595A
Authority: EP
Inventors: Peter David Thomas
Original assignee: Epwin Group PLC
Current assignee: Epwin Group PLC
Priority date: 1996-11-29
Filing date: 1997-11-27
Publication date: 1998-06-03
Also published as: GB2349409B; GB0015230D0; GB2349409A

Abstract

The invention provides a door leaf comprising a rigid frame (7) supporting a pair of outer skins (8), the frame being made of a timber-based material and having at one or more of its exposed edges an edging layer (10) made from a substantially water-impermeable material. The edging layer (10) can improve the appearance of the door leaf at its exposed edges and help to protect the frame from the ingress of moisture, without unduly compromising structural strength or ease of working. The invention also provides a door assembly incorporating this door leaf with an outer door frame, and a process for making such a door leaf or door assembly.

Description

Field of the Invention

This invention relates to a door leaf and to a door assembly incorporating the door leaf.

Background to the Invention

Known door leaves may be made from various materials, in particular timber. However, more recently so-called "composite" door structures have been developed, in which the leaf comprises a rigid frame (usually referred to as a "sub-frame") to define its outer edges, the frame being sandwiched between and serving to support two outer skins. The skins are typically made of a plastics material such as PVCu, ASA (acrylate styrene acrylonitrile) or ABS (acrylonitrile butadiene styrene). A composite door leaf may include a filling material, in the cavity defined between the outer skins, of an insulating and/or flame retardant material such as injection moulded foam.

The frame of such a composite door leaf may be made from a variety of appropriate materials. For instance, timber frames are known. However, these can cause problems when used with plastic skins, in that the expansion properties of the plastic and the timber are different, leading to internal stress, the uptake of moisture and ultimately rotting of the timber frame if not adequately sealed. The top and bottom frame elements are particularly vulnerable because, in use, they are more exposed to the atmosphere.

Frames made from extruded PVCu are also known. These suffer from the disadvantage that they cannot easily be trimmed to size and must therefore, ordinarily, be tailor made to fit any particular outer frame. Composite door leaves incorporating such frames can therefore be relatively complex and costly to manufacture. Moreover, a PVCu frame generally needs additional reinforcement to impart sufficient structural strength.

GB-A-2263129 discloses a composite door leaf having a frame made of a plastics material incorporating a reinforcing means typically of metal. The problems associated with this type of frame are that the linear thermal expansion of the materials used is quite considerable and very difficult to restrict. On a hot day, the door leaf could easily become wedged into its outer door frame, causing very real safety risks.

GB-A-2289708 discloses a composite door leaf in which the frame comprises top and bottom elements of structural foam overlying the ends of timber upright elements. The structural foam elements protect the vulnerable regions of the timber uprights from exposure to the weather.

GB-A-2296680 describes an extruded plastics composite, usable in the production of door and window frames, in which a base structure of extruded PVC has a surface layer (preferably co-extruded) of foamed polymethylmethacrylate. The surface layer can be used to provide a wood-effect finish.

Frames for composite doors may also be made of engineered timber-based materials, for instance laminar materials consisting of several thin layers of wood veneer glued together to make a rigid material which can then be cut and used as timber. Such a material is available, for instance, as "Intrallam L.S.L." (trade mark) from Trust Joist Macmillan. "Intrallam" is referred to as a "laminated strand lumber" and has a high tensile strength and a low moisture content, making it very resistant to twisting and bowing. It can be produced relatively economically and from a sustainable timber source. Such types of material can also generally be less water permeable, and hence more resistant to rot, than normal timber.

However, a composite door leaf having a frame made of such a laminar material is not without its disadvantages from the customer's point of view. The outer edges of the frame are visible between the plastic skins, and have an unorthodox appearance to the traditionalist, perhaps not as pleasing as, for instance, the edges of a timber or extruded PVCu frame. Customers also still tend to worry that a laminated timber frame will be permeable to water, and although in practice it is much less water permeable than normal timber, nevertheless it is not completely resistant to rot in the way that, for instance, a PVCu frame would be (especially if it is worked prior to use and not subsequently resealed).

Statements of the Invention

According to a first aspect of the present invention there is provided a door leaf comprising a rigid frame supporting a pair of outer skins, the frame being made of a timber-based material and having at one or more of its exposed edges an edging layer made from a substantially water-impermeable material.

The edging layer can improve the appearance of the door leaf at its exposed edges and also help to protect the frame from the ingress of moisture. However, since the frame is still essentially made of a timber-based material, it retains all the advantages associated with the use of such materials, such as structural strength, economic production and ease of working.

The term "door" here includes any similar closure member such as a hatch. It also includes a door incorporating one or more glazed window panels.

The frame is preferably made from a laminar timber-based material. One example of such a material is a laminated strand lumber such as "Intrallam" (trade mark), described above. Other suitable materials may be referred to as "engineered timbers". The frame will be made substantially of the timber-based material, although it may also include relatively small regions of other materials and it does also of course carry the substantially water-impermeable edging layer.

The exposed edges of the frame are those which are visible around the outside perimeter of the door leaf between the outer skins. The edging layer ideally covers all exposed edges, ie at the top, bottom and sides of the in-use door leaf. However, it may only cover the side edges (which will typically be vertical when the door leaf is in use), since these are the edges for which visual appearance is most important.

The edging layer must be made of a material which is substantially water-impermeable, by which is meant that, for practical purposes, it resists penetration by water. It should certainly be less water-permeable than the timber-based material from which the frame is otherwise made. Examples of suitable materials include medium density fibreboard (MDF) and various plastics materials such as, for instance, extruded PVC or polythene, or those materials known variously as structural foam, blown styrene, foamed styrene or polystyrene (or mixtures thereof) and toughened polystyrene. Foamed materials can be especially suitable because they have a cellular structure which is particularly impermeable to water. They are generally rigid materials produced by extrusion processes.

Suitable available products include those known as "Timbron", "Envirowood" and "Amari Foam" (trade marks), but this list is by no means exhaustive. Such materials are often known as "composite plastics".

Preferred characteristics for the edging layer material include a density of from about 0.4 to 1.0 g/cm³, preferably from about 0.65 to 0.8 g/cm³, most preferably about 0.8 g/cm³ and a water absorption capability of about 1.0% or lower, preferably about 0.5% or lower, more preferably about 0.2% or lower, most preferably about 0.1% or lower. It should ideally be impact resistant, to at least the same or a similar degree to that of the timber-based material from which the frame is made, so that the edging layer does not compromise the strength of the overall door leaf. "Impact resistant" here means sufficiently strong to withstand normal use in the finished door leaf, ie, the door leaf can be opened and shut in an outer frame without risk of breaking the edging layer. In the case of a foamed material, impact resistance can be affected by factors such as its density and the extent to which the material is worked prior to attachment to the timber-based frame.

The edging layer should also be made of a material which is relatively easy to cut and work, which ideally has a pleasing appearance to the eye of the typical customer. It may of course have a plain or patterned appearance - it may for example have a "wood-effect" finish, to give the impression that the door leaf is made of timber.

A door leaf according to the invention may incorporate more than one type of edging layer material; it may for instance have MDF edging layers at the top and bottom exposed edges of the frame, and blown styrene edging layers at the sides, or any other suitable combination of edging materials.

The edging layer may be secured to the exposed edge(s) of the frame in any appropriate manner. Preferably it is laminated to the frame, for instance using a hot melt adhesive or a contact adhesive. Such an adhesive should ideally provide excellent adhesion to all the materials used, at least a degree of water resistance, a useable temperature range of between about -10°C and about 30°C, and at least a degree of impact resistance. Many suitable adhesives are commercially available and can be used in conventional fashion.

The securing of the edging layer to the frame can conveniently be carried out at an early stage in the manufacture of the door leaf, prior to the addition of the outer skins or even to assembly of the frame (the edging layer then being sandwiched between the skins in the finished product).

For additional protection against the ingress of moisture, an additional membrane, for instance of waterproof tape, may be incorporated between the timber-based material and the edging layer at one or more of the exposed edges, in particular along the top and bottom edges of the in-use door leaf. Examples of suitable waterproof tapes include high tack adhesive tapes such as "Technibond" (trade mark), which comprises a closed-cell, cross-linked, white polyethylene foam coated with an aggressive pressure-sensitive high tack adhesive. Similar tapes are available from various double-sided tape manufacturers. The additional membrane may alternatively comprise a thin layer of extruded PVC or other plastics material.

A double-sided adhesive strip may alternatively be used to secure the edging layer to the frame - this would usually provide an additional water barrier and hence obviate the need for an additional membrane. Some adhesives, eg, some hot melt adhesives, can themselves function as water barriers, and again in such a case there may be no need for an additional membrane.

The thickness of the edging layer may vary according to requirements. It need only be very thin, sufficient to alter the appearance of the exposed edge(s) and give protection against moisture. However, a thicker edging layer may be used if the door leaf is to be sold on to a customer who wishes subsequently to cut it to size to fit into a particular door frame. Conveniently, the thickness of the edging layer will vary between about 5 mm and 20 mm for a typically-sized door leaf, more preferably between about 8 and 18 mm, most preferably about 13 mm. This edging layer might later be trimmed by up to about 5 mm to fit in an outer door frame.

It is in any case preferable that the thickness ratios of the edging layer and the timber-based frame be such that the inclusion of the edging layer does not substantially reduce the strength of the frame as a whole. Preferably, the thickness of the edging layer is no greater than 25%, more preferably no greater than 20% and most preferably between about 9% and 17%, of the overall thickness of the frame (ie, the combined timber-based frame and edging layer).

The door frame can conveniently be made from lengths of timber-based material (with edging layer attached) secured together to form appropriately spaced corners. The corners may be mitred in conventional fashion, and the frame components secured together at the corners using standard fastening means, such as an adhesive and a "Hoffmann" butterfly cleat or dovetail key for instance. The properties required of the adhesive are similar to those of the frame-to-edging layer adhesive.

More preferably, the angle of the mitre at a corner will differ from the conventional 45°, and will be chosen so that the outer end of the mitre join intersects the outer surface of the edging layer not at a corner but a small distance away from it. This distance may be anything up to the thickness of the edging layer, and is preferably between about 2 mm and about 10 mm, more preferably between about 4 mm and about 8 mm, most preferably about 6mm. This provides aesthetic advantages if the door leaf needs to be trimmed to a desired size prior to use. A "witness line", or seam edge, can appear along the side edges of the door leaf if the edging layer is trimmed away in the vicinity of a 45° mitre. This is unsightly. If, however, the mitre join is offset from the frame corner by a distance at least as great as the amount trimmed from the edging layer, any witness line can be made to occur along the top or bottom edge of the in-use door leaf, which is rarely seen in normal use.

Other aspects of the door leaf may be entirely conventional. For instance, it may comprise a filling material positioned between the outer skins. Such a material could be, for instance, cut or injection moulded foam, or could comprise a foam material injected into the cavity between the outer skins. The foam could for instance be a polyurethane foam or a polystyrene foam. Such filling materials, and methods of incorporating them into composite door leaves, are already known. One typical example of a suitable filling material is that available as "Foamstrand" (trade mark), a foamed polyurethane containing reinforcing strands.

The outer skins will typically be made of a plastics material, preferably a thermoplastic such as PVCu, ASA or ABS, which conveniently can be vacuum formed to the desired profile so as to define window openings and the like. The skins may be attached to the frame in any conventional manner - typically, adhesive will be applied between the skins and the frame and the three components pressed together.

According to a second aspect of the present invention there is provided a door assembly incorporating a door leaf in accordance with the first aspect, together with an outer door frame. Other components may be included in the assembly, for instance hinges to mount the door leaf in the outer frame, draft excluders and the like.

In the case of both the first and second aspects of the invention, the door leaf may include the usual types of door furniture such as letter boxes, door knockers, handles and any appropriate type of locking mechanism. Such components, and the ways of attaching them to composite door leaves, are well known in the art.

According to a third aspect, the invention provides a process for making a door leaf or door assembly according to the first or second aspect, comprising attaching a substantially water-impermeable edging layer to one or more exposed edges of a rigid timber-based frame, and attaching to the frame a pair of outer skins.

The present invention will now be described by way of example only and with reference to the accompanying illustrative drawings, of which:

Fig.1 is a front view of a door assembly in accordance with the present invention;

Fig. 2 is a front view of the frame forming part of the door leaf illustrated in Fig. 1;

Fig. 3 is a schematic cross-section taken through the line A-A in Fig. 1, omitting the outer door frame;

Fig. 4 is a cross-section taken through the line B-B in Fig. 1, again omitting the outer frame;

Figs. 5 and 6 are schematic cross-sections analogous to those of Figs. 3 and 4 respectively, but showing the outer frame as well;

Fig. 7 is a section of the type shown in Fig. 3, through part of an alternative door leaf according to the invention; and

Fig. 8 is a front view (not to scale) of a frame for an alternative door leaf in accordance with the invention.

Detailed Description of the Drawings

The door assembly shown in Fig. 1 comprises a door leaf generally labelled 1 mounted in an outer frame 2. The door leaf in this case incorporates one or more glazed panels such as 3 and conventional door furniture such as handle 4, a lock and hinges by which the leaf is mounted into the outer frame 2.

The construction of the door leaf 1, in accordance with the present invention, can best be seen with reference to Figs. 2-4. It comprises a frame generally labelled 7 sandwiched between, and supporting, two outer skins 8 (see Figs. 3 and 4). The frame 7 is essentially made of a laminar engineered timber material 9, of cross section approximately 40 mm x 72 mm. Around its entire perimeter, ie covering its exposed edges, the main frame 9 carries an edging layer 10 made from, in this case, a foamed medium impact styrene/polystyrene compound. This edging layer, of about 13 mm nominal thickness, gives a more pleasing appearance to the edges of the door leaf as seen in use, and also provides a degree of protection to the main frame 9 against the ingress of moisture.

The overall "thickness" of the timber-based frame with its plastics edging layer is approximately 85 mm (ie, 72 mm for the timber-based frame and 13 mm for the edging layer). These are dimensions suitable for a conventional door, but others are of course possible, depending on the use to which the door leaf is to be put. "Slimline" doors may for instance have a timber-based frame of 57 mm or even 47 mm nominal thickness (ie, total frame thickness, with a 13 mm edging layer, of 70 mm or 60 mm respectively).

The material from which edging layer 10 is made is a mixture of crystalline styrene and high impact polystyrene, in an approximate ratio of 2:1. It is foamed using a chemical blowing agent (such as CO₂) to produce a rigid extruded cellular product. The foaming yields an overall density of between about 0.65 and 0.8 g/cm³, as compared to the density of crystalline styrene alone which is 1.05 g/cm³.

In this case the material is specially pigmented to give a wood-like appearance. It may of course be fireproofed or otherwise treated, according to requirements.

Its physical characteristics are as follows:

PROPERTY	UNIT	TEST METHOD	RESULT
Melt Flow Rate	g/10 mins	ISO 1133 Condition 8H (200°C/5Kg)	3.0
Izod Impact Strength	kJ/m²	ISO 180/1A @ 23°C	5.0
Flexural Modulus	Mpa	ISO 178	2700
Vicat Softening Point	°C	ISO 306/A	100

Since styrene can absorb a maximum of only 0.1 % of water, and water impermeability can be increased by foaming, this material makes a very effective moisture barrier when used as an edging layer in a door leaf according to the invention.

When the material is extruded, a hard glossy skin of denser solid styrene/polystyrene is formed around its perimeter. This skin can be removed from three of the four sides by machining, but retained on the fourth side (which will be bonded to the timber-based frame 9) to act as a moisture impermeable barrier.

Note that in Figure 2, the edging layer 10 is shown exaggerated in size relative to the timber-based frame 9, for clarity.

Referring now to the cross-sections shown in Figs. 3 and 4, it can be seen how the frame 7 is sandwiched between the two outer skins 8 (made from vacuum-formed ASA/ABS or, if more appropriate, PVCu). The skins 8 are glued onto the frame 7.

The edging layer 10 is laminated to the timber-based frame 9 using a hot melt adhesive such as that available as "Protak 342" (trade mark), a high heat resistance hot melt adhesive useable with ABS, PVC, plastic laminate and wood veneer. The material for the edging layer is typically available in the form of 18 mm width extrusions - these are adhered to the timber-based material prior to construction of the frame 7 (four frame elements, each made of timber-based material edged with the foamed styrene/polystyrene, can be cut and mitred to size and then secured together at their corners to complete the frame). The edging layer is then typically machined down to a 13 mm nominal width, which can be further trimmed by up to about 5 mm by a customer wishing to hang the door leaf in his own outer door frame.

A layer of polyurethane foam 11 is sandwiched between the two outer skins 8, providing cushioning and support therefor and also a high degree of thermal insulation across the door leaf. The foam might be, for instance, "Foamstrand" (trade mark), a material described in UK patent No 2280467 which is made up of a foamed polyurethane containing reinforcing strands. The reinforcing strands may be made from offcuts generated during the manufacture of plastics, timber or engineered timber door frames. The foam is usually injected into the cavity between the outer skins 8, after introduction of the reinforcing strands. Such a material offers increased resistance to, eg, knife attack and so makes the door leaf more secure.

Note that the outer frame 2 has been deliberately omitted from Figs. 3 and 4, for clarity.

Figs. 5 and 6 are cross-sections through the entire door assembly of Fig. 1, showing how the door leaf is mounted in conventional outer frame 2.

Fig. 7 illustrates how an alternative door leaf in accordance with the invention incorporates a layer of a waterproof tape 12, between its timber-based frame 9 and its outer edging layer 10. Other parts of the door leaf correspond to those of the leaf shown in Fig. 3, and are labelled with the same reference numerals.

Finally, the embodiment illustrated in Fig. 8 has a preferred form of mitred corners. The angle of the mitre differs from the usual 45°, and in this case is chosen so as to provide a nominal 6 mm clearance between the corners of the frame and their respective mitre cuts 14. Thus, if the 13 mm edging layer 10 is trimmed by up to 6 mm at the sides of the door (as shown by the dotted lines 15), so as to produce a door leaf of a desired size, the "witness line" or seam caused by the mitred join will only be visible along the top and bottom edges of the door leaf, and not along the side edges which would be seen in use. The trimmed door leaf can then have a more pleasing appearance than would be possible using a conventional mitred corner.

Users would normally be advised to trim no more than about 4 or 5 mm from the edging layer 10.

At the top left hand corner of the Fig. 8 frame, a conventional 45° mitre is illustrated. The "witness line", which would become visible on trimming the door leaf, is designated 16.

The four frame components are secured together, at the mitred corners, using an adhesive and a plastic "Hoffmann" butterfly cleat, as shown at 17. The adhesive used is typically "Apollo A.3328" (trade mark), a polystyrene solvent weld adhesive formulated for bonding together polystyrene components.

Note that the frame and edging layer are shown greatly exaggerated in size in Fig. 8, as is the mitre offset, for illustrative purposes.

A door leaf in accordance with the invention may of course be sold alone or as part of a complete door assembly such as that illustrated in Fig. 1.

Claims

A door leaf (1) comprising a rigid frame (7) supporting a pair of outer skins (8), the frame being made of a timber-based material (9) and having at one or more of its exposed edges an edging layer (10) made from a substantially water-impermeable material.
A door leaf according to claim 1, wherein the frame is made of a laminar timber-based material.
A door leaf according to claim 1 or claim 2, wherein the edging layer is made from a blown or foamed styrene, polystyrene or mixture thereof.
A door leaf according to any one of the preceding claims, wherein the material from which the edging layer is made has a water absorption capability of about 1% or lower.
A door leaf according to any one of the preceding claims, wherein the thickness of the edging layer is between about 5 and 20 mm.
A door leaf according to any one of the preceding claims, comprising lengths of timber-based material, to which the edging layer has been attached, secured together to form appropriately spaced corners, wherein at least one of the corners is formed using a mitre join (14) and wherein the outer end of the mitre join intersects the outer surface of the edging layer at a line offset from the corner of the door leaf.
A door leaf according to claim 6, wherein the outer end of the mitre join intersects the outer surface of the edging layer along the top or bottom of the in-use door leaf.
A door assembly incorporating a door leaf according to any one of the preceding claims together with an outer door frame (2).
A process for making a door leaf or door assembly, comprising attaching an edging layer (10) made from a substantially water-impermeable material to one or more exposed edges of a rigid timber-based frame (9), and attaching to the frame a pair of outer skins (8).
A process according to claim 9, comprising the steps of securing together two or more lengths of a timber-based material and attached edging layer, to form appropriately spaced corners of a rigid frame, wherein at least one of the corners is formed using a mitre join in such a way that the outer end of the mitre join intersects the outer surface of the edging layer at a line offset from the corner of the finished door leaf.